With reference to FIG. 1, a solar collector is a device capable of heating a working fluid by sunlight, and the solar collector generally comprises a plurality of parallel evacuated tubes 10, two collecting tubes 20/30 coupled perpendicular to both ends of each evacuated tube 10 respectively, and the evacuated tubes 10 are provided for receiving sunlight. In general, a metal fin 40 is soldered to each evacuated tube 20/30, or a fin 40 is soldered between two evacuated tubes 20/30, and a working fluid at room temperature is entered from one of collecting tubes 30 and then diverted to each of the evacuated tubes 10 for exchanging heat with the evacuated tubes 10, and finally exited from another collecting tube 20.
However, the conventional flat panel solar collector still has the following drawbacks. The thermal resistance at a contact between the fin 40 and the evacuated tube 10 is very large, and thus affecting the thermal conductivity adversely. In addition, the fin 40 is very thin, so that a significant drop of thermal conducting efficiency of the fin 40 usually occurs at both linear ends of the fin 40 in contact with the evacuated tube 10, so that the wider the fin 40, the smaller is the heat transfer of the evacuated tube 10 per unit area of the fin 40. In present existing structural designs, the only improvement that can be made is to increase the number of evacuated tubes 10 in order to decrease the spacing between the evacuated tubes 10, and thus decreasing the width of the fin 40 to enhance the thermal conducting efficiency of the fin 40. However, such improvement still cannot overcome the problem of a large heat resistance at the contact between the fin 40 and the evacuated tube 10.